The present invention relates to an inkjet printer, and in particular, to an inkjet printer wherein effectively restricted is deterioration of quality of printed images, due to viscosity reduction of ink by temperature change and also due to structural differences of variation of structural parts.
Inkjet printers perform image printing in the following manner: the inkjet printer jets small ink droplets, from a plurality of nozzles which are integrally formed in a recording head, onto a recording media such as a paper sheet, to land the ink droplets on the paper sheet, and further the inkjet printer produces printed images on a predetermined recording surface of the recording media, via driving the recording head in the main scanning direction across the width direction of the sheet. In such an inkjet printer, if there is any displacement of the deposited ink droplet jetted from the nozzles of the recording head driven in the main scanning direction, the recorded images includes turbulences, resulting in deterioration of image quality. Accordingly, the jetting velocity must be precisely controlled.
Generally, ink viscosity changes due to temperature, whereby ink viscosity changes due to temperature of the recording head as well as the ambient temperature. Since the jetting velocity of the ink droplet varies by the change of the ink viscosity, the number of jetted droplets also varies, which results in the change of image density, and further, the change of the landing position generates unclear images, which are unacceptable images.
Yet further, temperature characteristics of the various mechanical or electronic parts structuring the inkjet printer vary, and in addition, since each inkjet printer has its own structural difference, changes in image density due to these structural differences result in image deterioration.
In the past, in order to overcome the above-mentioned image deterioration, proposed was technology wherein the ink droplets jetting velocity was measured, and driving conditions of the recording head were controlled by the measured velocity (Patent Documents 1, 2 and 3). Further proposed is technology wherein the ink droplets jetting velocity and weight of ink droplet are measured, and driving condition of the recording head is controlled by the measured droplet velocity and weight (Patent Document 4). Yet further proposed is technology wherein the ink droplets jetting velocity and weight are measured, and the driving condition of the recording head is controlled by the measured velocity and weight (Patent Document 5), while yet further proposed is technology wherein the ink droplets jetting velocity is measured, and a heater to heat the ink is controlled, whereby the ink viscosity is controlled (Patent Document 6).
[Patent Document 1] JP-A 9-174835
[Patent Document 2] JP-A 11-300944
[Patent Document 3] JP-A 2003-39667
[Patent Document 4] JP-A 11-300964
[Patent Document 5] JP-A 2003-94629
[Patent Document 6] JP-A 2003-136696
[Patent Document 7] JP-A 2003-191467
As Patent Documents 1-7 show, when the driving condition of the recording head is controlled by the ink droplets jetting velocity, to correctly secure the ink droplets jetting velocity which tend to change, the ink droplets jetting velocity must be measured frequently. However when it is measured during printing, continuity of the density at that time point may be altered. Still further, in order to correctly measure the ink droplets jetting velocity, measurement must be conducted while the ink jetting condition of the recording head is maintained in good condition, in which it takes a long time to measure the ink droplet jetting velocity. Accordingly the driving condition of the recording head cannot be frequently controlled by the ink droplets jetting velocity.
On the other hand, without measuring the ink droplets jetting velocity, but depending on temperature characteristics of ink viscosity, by measuring ambient temperature or recording head temperature, the driving condition can be controlled by those measured results. Since this case differs from the case of controlling by the ink jetting velocity, there is no need to measure the velocity while the ink is practically jetted, and which can be conducted while image printing, and further the time interval between temperature measurement and the control of driving condition of the recording head can be shortened, which is an advantage for securing continuity of density. However, this method includes difference of temperature characteristics of a thermal detector, ink viscosity and a circuit board, and in addition, there is variation due to structural differences or ink changes, which cause changes of density, therefore, correct control is difficult in practice.
In addition, Patent Document 7 teaches that the ink droplets jetting velocity is controlled by a relationship table between the ambient temperature and the ink droplets jetting velocity, however, the driving condition is corrected only when the ink droplets jetting velocity is detected, which does not solve the above described problems.
Accordingly, in the present invention, the problem is to provide an inkjet printer, wherein solved are various problems in the ink jetting velocity control by measuring velocity or temperature, wherein printing is continuously and stably conducted, independent of structural difference and ambient differences, and wherein excellent image quality continuously results.